The present invention relates generally to document feeders, and, more specifically, to document feeders in commercial high speed document processing equipment.
Document feeders are common in various types of equipment in which a stack of documents or sheets of paper are to be processed one-by-one in sequence. Common sheet feeders are found in copying machines and fax machines which typically operate at relatively low sheet feeding speeds.
As the feeding speed increases, the document feeders configured therefor typically increase in complexity and cost in view of the increased difficulty associated therewith. For example, banking institutions or other processing centers use sophisticated check processing machines for reading, imaging, encoding, and sorting commercial checks at considerable speed. Four hundred checks or documents per minute (400 dpm) carried through the processing machine is a relatively high rate which is typically maintained continuous for one or more business operating shifts per day.
The checks are loaded in stacks into a hopper portion of the machine which individually transports the checks in turn through the remainder of the machine along a check feedpath defined by driven rollers and belts and associated guiding elements. A controller in the form of a digitally programmable computer controls the entire operation of the machine including the speed of the various motors driving the various transport rollers and belts for maximizing check processing throughput, without unacceptable jamming of the checks or other malfunctions in any one of the modules of the machine.
Optical sensors are disposed along the entire check feedpath through the machine for detecting the presence of the checks and the motion thereof for use in controlling operation and detecting any jamming which may occur. Malfunction or jamming must be instantaneously detected by the sensors for correspondingly interrupting operation of the driving motors to limit the adverse affects thereof.
Any interruption in normal operation of the check processing machine correspondingly reduces its effective check processing throughput, and is commercially undesirable as a loss of valuable processing time with a corresponding increase in associated costs.
Maximum throughput of the series of checks transported through the machine is limited in practice by a minimum desirable spacing or gap between the traveling checks. For example, the encoding module of the machine must have sufficient time to print along the bottom edge of the check a suitable code indicative of the check processing or clearing operation.
Correspondingly, the desired processing throughput rate controls the maximum gap between traveling checks since the checks may be more widely spaced apart at slower transport speeds if desired.
Nevertheless, it is common practice to use the optical sensors in the machine for determining intercheck gaps during operation and adjust those gaps as desired. Since relatively large gaps provide sufficient time for processing each check in each of the various modules of the machine, the control thereof does not require either high precision or fast response. For example, one check processing machine enjoying years of successful commercial use in this country is designed for a throughput rate of about 400 checks per minute for continuous operation of the machine without malfunction or jamming due to excessively small intercheck gaps.
Commercial checks vary in length from about 4.8-9 inches (12.2-22.9 cm) in length and about 2.75-5 inches (7-12.7 cm) in width or vertical height. With a nominal check length of about 6 inches (15.2 cm) a nominal intercheck gap of about 9 inches (22.9 cm) will occur at the 400 dpm throughput rate. This relatively large gap may be effectively measured by optical sensors placed several checks downstream in the feedpath from the inlet hopper tray. Measurement of the size of the downstream gaps may be used to adjust gap size upstream therefrom, typically by intermittently halting operation of the advance drive motor for correspondingly increasing intercheck gaps as desired.
However, in a higher speed check processing machine being developed, the nominal intercheck gap is closer to the minimum permitted value for the machine which can therefore randomly result in occasional intercheck gaps less than the permitted minimum. When sub-minimum gaps occur, downstream monitoring sensors can lead to operational warnings or automatic interruption in the check processing machine requiring remedial correction. And, sub-minimum gaps may also cause undesirable jamming of the checks which also requires remedial operator intervention which substantially reduces the overall throughput rate of the machine during use.
Accordingly, it is desired to provide an improved document feeder and method of operation for actively controlling interdocument gaps.
A document feeder includes advance, separation, and transport rollers for driving documents in turn along a feedpath from an input tray containing a stack of the documents. A sensor is disposed between the separation and transport rollers for detecting presence of the documents therebetween. A controller is joined to the rollers for controlling speed thereof, and is operatively joined to the sensor for measuring interdocument gaps between the separation and transport rollers. The controller actively adjusts the interdocument gaps by temporarily changing speed of the separation roller at the beginning of the feedpath near the input tray. The interdocument gaps are measured and corrected between the separation and transport rollers for precise control thereof while maximizing throughput.